In the medical arts, catheters are frequently used to diagnose and treat various disorders in a patient, such as clogged or blocked blood vessels. A catheter is introduced into a blood vessel of a patient by, for example, making an incision in the patient over the blood vessel and inserting the catheter into the blood vessel of the patient. A catheter operator such as a physician then maneuvers the catheter through the blood vessels of the patient until the catheter is properly situated to diagnose or treat the disorder. Since maneuvering a catheter within a patient can sometimes be a difficult task, requiring a high degree of care and time taken to change the position of the catheter, a type of catheter known as a telescoping catheter is frequently used to perform these diagnoses and treatments.
Conventional telescoping catheters include two basic components which are designed to telescope in relationship to each other. The first component includes a drive cable with a medical device such as an ultrasonic transducer or other imaging device mounted on the distal end of the cable. The proximal end of the cable is attached to a housing at the proximal end of the catheter. This housing contains components adapted to interface the drive cable with a power source, as well as other components, such as a flush port for introducing liquid solutions into the catheter, or other components useful to aid a physician or other operator in effectively and efficiently using the catheter to diagnose and treat a patient.
A proximal portion of the drive cable is covered by a flexible proximal sheath, which is attached to the proximal end of the catheter. This proximal sheath shields the drive cable from the external environment, thereby preventing contaminants from entering the patient via the catheter. The sheath also provides support for the drive cable, to restrain the drive cable from excessive flexing, bending, or other undesirable changes in location or angle.
The second component includes a flexible distal sheath which covers the distal portion of the drive cable. The distal end of the distal sheath may be sealed shut to prevent the distal end of the drive cable from contacting the patient directly, or it may be open, to allow the distal end of the drive cable to protrude out through the distal sheath and into the patient. This distal sheath also shields the drive cable from the external environment and provides support for the drive cable, as described above.
The proximal sheath and drive cable are adapted to telescope in relationship to the distal sheath. The telescoping relationship allows the catheter operator to move the first component including the medical device proximally and distally within the catheter, without having to move the entire catheter within the patient. This allows the catheter operator to easily change the location of the medical device within the patient.
In order to prevent the interior of the catheter from being exposed to the external environment, conventional telescoping catheters are designed to stop the telescoping movement of the proximal sheath away from the distal sheath before the proximal end of the distal sheath disengages from the distal end of the proximal sheath. For example, where the proximal sheath telescopes inside the distal sheath, the proximal end of the distal sheath may have a lip or detent extending inwardly, to catch against a corresponding lip, detent or flare on the distal end of the proximal sheath, and thereby prevent the proximal and distal sheaths from disengaging from each other. Alternatively, where the distal sheath telescopes inside the proximal sheath, the distal end of the proximal sheath may have a lip or detent extending inwardly, to catch against a corresponding lip, detent or flare on the proximal end of the distal sheath.
In order to accommodate the lip, detent or flare on the end of the innermost of the two sheaths, and still allow the two sheaths to telescope in relationship to each other, the internal diameter of the outermost of the two sheaths must be large enough to allow the lip, detent or flare to travel unimpeded along the inside of the outermost of the two sheaths. Therefore, the internal diameter of the outermost of the two sheaths is substantially larger than the external diameter of the drive cable extending along the inside of both of the sheaths.
When the telescoping catheter is fully compressed, this does not pose a problem, as the innermost of the two sheaths, whose internal diameter is only slightly larger than the external diameter of the drive cable, provides the desired support for the drive cable. However, as the telescoping catheter is being extended, the innermost sheath is retracted from covering the drive cable, leaving only the outermost sheath to provide support and protection to the drive cable. Since this outermost sheath is substantially larger in internal diameter than the external diameter of the drive cable, the drive cable is substantially unsupported and unprotected within the catheter.
Therefore, there is a need for an improved telescoping catheter.